Evaluation of a model which predicts whole plant respiration from photosynthesis and biomass

Abstract

Over time, whole plant growth is nearly the balance between photosynthesis and respiration. This research consisted of devising and testing a model which predicts plant respiration rates from knowledge of the photosynthesis rate and initial weight of the biomass, on an instantaneous basis. Parameter determination, establishment of initial conditions, calculations of photosynthesis rate, and model testing were carried out using only carbon exchange rate (CER) data and the final dry weight in carbon equivalents. The model considers the plant to consist of two quantities, the photosynthate pool (POOL) and the structural dry matter (SDM). These are acted upon by three processes: photosynthesis, SDM synthesis, and SDM maintenance. Photosynthesis fills the POOL. A fixed fraction of the POOL, the yield of growth (YG), is converted to SDM. The remainder provides energy for SDM synthesis and is respired as growth respiration. SDM synthesis proceeds at a rate proportional to POOL size until a maximum growth rate (MAXGRO), proportional to SDM is reached. When SDM synthesis is less than MAXGRO, POOL usage rate is determined by the POOL efflux coefficient (E), a fraction of POOL per hour. Energy costs for maintaining SDM are borne by SDM, giving rise to maintenance respiration. This is described by the maintenance coefficient (B), a fraction of SDM per hour. Previous research has shown that a plant grown in a constant light and temperature regime will reach a state where no net change in POOL occurs over a light-dark cycle. In this state, a plant's daily respiration was found to equal (1-YG) of the daily photosynthesis plus a fraction of the plant biomass in carbon equivalents. Simulation studies indicated this model can replicate these findings. The model is dynamic and can predict plant growth and respiration even if POOL varies due to changes in photosynthesis rate. Additionally, observed effects ofPOOL size on photosynthesis were replicated...